This disclosure generally relates to systems and methods for generating air traffic arrival schedules.
The Next Generation Air Transportation System (NextGen) and Single European Sky ATM Research (SESAR) programs seek to implement a trajectory-based operations concept that requires substantial changes to the current air traffic management (ATM) system, in both equipment and procedures. It is expected that required airplane capabilities for trajectory-based operations will include four-dimensional (4-D) trajectory execution with lateral and vertical navigation performance bounds, as well as navigation to a required or controlled time of arrival (CTA) at one or more points in space, and/or airplane traffic situation awareness with interval management applications. Limitations to the deviations of these 4-D trajectories will be required in order to avoid conflicts between merging, in-trail and crossing traffic. Additionally, due to traffic growth, airport throughput will have to be improved so arrival time accuracy will become more stringent. At the same time, the improved predictability of trajectory-based operations should reduce fuel consumption and the environmental impact by planning Continuous Descent Operations (CDOs) as much as possible with minimal tactical interventions to solve conflicts.
It is envisioned that NextGen and SESAR air traffic management (ATM) systems will enable aircraft to be at much closer longitudinal/lateral spacings in all phases of flight in controlled and uncontrolled airspace to increase airspace capacity and efficiency. These new airspace environments will be enabled by Automatic Dependent Surveillance-Broadcast (ADS-B) technology along with other technologies. ADS-B enhances safety by enabling display of traffic positions and other data, in real-time, to Air Traffic Control (ATC) and to other appropriately equipped ADS-B aircraft with position and velocity data transmitted every second. The ADS-B system relies on two avionics components—a high-integrity GPS navigation source and a data link (ADS-B unit) connected to other aircraft systems. ADS-B enables a pilot to display traffic information for surrounding aircraft, including the identification, position, altitude, heading and groundspeed of those aircraft. However, not all aircraft are equipped with an ADS-B system.
With the introduction of new ATM systems, the flight crew will be given responsibility for achieving and maintaining spacing behind other aircraft for higher airspace efficiency and capacity in all phases of flight. To achieve higher airspace efficiency and capacity, ATC operations will work to decrease spacing and also maintain consistent spacing between all ADS-B-capable aircraft. One of the procedures that will be utilized in achieving this goal will allow the air traffic controller to provide instructions to the flight crew to position their aircraft (hereinafter “trailing aircraft”) behind a preceding aircraft (hereinafter “leading aircraft”) at a specified longitudinal spacing interval defined in either time or distance. Once the clearance has been accepted, it will be the trailing aircraft flight crew's responsibility to achieve and then maintain the specified spacing value behind the leading aircraft as instructed by the controller.
The main arrival operations concept proposed for NextGen encompasses strategic optimization of the traffic flow using ground automation capabilities prototyped by NASA, namely, Traffic Management Advisor and Efficient Descent Advisor. Traffic Management Advisor (TMA) is the traffic scheduling and sequencing tool in charge of building conflict-free arrival sequences at runways and at a set of predefined metering fixes (i.e., a fix along an established route from over which aircraft will be metered prior to entering terminal airspace). The latter are typically located at the entry of the terminal area, such as in Terminal Radar Approach Control (TRACON) facilities. Efficient Descent Advisor (EDA) is the meet-time advisory tool that issues speed and path instructions to aircraft to meet the scheduled arrival time at the metering fixes set by the TMA. For independent arrival-departure operations, the scheduled inter-arrival time at the runway (or final approach fix) is typically based on wake-vortex criteria and weather conditions, resulting in fixed spacing (in distance or time) per pair of aircraft category types. At the metering fix, the planned spacing gap is typically based on a fixed miles-in-trail criterion independent of the trailing aircraft types.
On the airborne side, most commercial aircraft are equipped with Flight Management Systems (FMS) that offer automated vertical navigation (VNAV) with different modes. In descent, aircraft typically fly VNAV PATH, a mode where the aircraft uses a path-on-elevator method to track the vertical reference profile while throttles typically remain idle. From an energy point of view (assuming the aircraft mass is accurate), the aircraft is tracking the reference potential energy while the engines keep the reference idle power. According to the principle of energy conservation, any unexpected energy deviations (for example, wind energy prediction errors) will affect the kinetic energy. Hence the groundspeed of the aircraft changes, resulting in deviations in the position of the aircraft over time. More advanced guidance methods, like the Required Time of Arrival (RTA) method, combine VNAV PATH with path recalculations in order to meet a target time at a given waypoint. Other 4-D guidance methods track the groundspeed reference with the elevator pushing all errors into the vertical profile. For example, the supplemented Continuous Descent Approaches for Maximum Predictability (CDA-MP) guidance technique is an automated version of the manual crew-in-the-loop version disclosed by Garrido-Lopez et al. in “Analysis of Aircraft Descent Predictability: Implications for Continuous Four-Dimensional Navigation,” AIAA Guidance, Navigation, and Control Conference, AIAA 2011-6217, Portland, Oreg. (2011), which features periodic speed adjustments to maintain the continuous 4-D tracking. Some guidance methods apply energy corrections through some use of the spoilers and throttles, or the timing of the aircraft landing configuration. Alternatively to the above-mentioned absolute time-based guidance methods, relative (time-based) guidance techniques are being developed that manage the aircraft's own position relative to a leading aircraft. An example of such a Flight deck Interval Management (FIM) system is the Airborne Spacing for Terminal Arrival Routes (ASTAR) system developed by NASA. Besides the various FMS guidance logics, also other factors influence the 4-D trajectory confinement in time and space, like the accuracy of the wind prediction, which may vary per FMS type and per airline.
Arrival management systems, like TMA, have been deployed at various airports over the world. These existing systems sequence flights to the runways and a set of metering fixes with the goal of predicting the optimal sequence in order to maximize runway throughput. The resulting arrival schedule is used by air traffic controllers today primarily as a guideline. The addition of strategic intent advisory tools like EDA (and others around the world) to the arrival management concept is currently still in a prototyping and validation phase. Adding spacing buffers into the scheduling algorithm has been proposed in research, but only fixed spacing buffers independent of the FMS equipage type and arrival demand have been evaluated so far. In today's operations without the advanced ground automation systems or advanced 4-D FMS guidance, CDOs have been implemented in some airports using customized arrival procedure design and an optimal inter-aircraft spacing target at the beginning of the arrival procedure as an advisory for the air traffic controllers to condition the traffic. This optimal initial spacing was determined offline with a Monte Carlo simulation for different levels of CDO success rate and per specific pair of trailing aircraft types. Hence these spacing buffers are based on differences in aircraft type performance rather than FMS guidance equipage. This method works satisfactory for trailing aircraft flying the same or similar routes, but is more difficult to be applied to arrival routes merging from different arrival directions. The latter requires ground automation to be in place.
The global operational aircraft fleet has a mix of aircraft guidance capabilities and with that comes variability in achievable arrival time accuracies. There is a need for improved means and methods for scheduling arrival traffic at airports which take into account the different FMS equipage onboard different types of aircraft.